Optical instrument and method of making same



June 1.9, 1945.' Lc. GARDNER vOPTICAL INSTRUMENT AND METIHOD OF MAKING SAME.

Filed May 15, 1942 3 Sheets-Sheet l Irvine Gardner @M W 7@ 7( M Arma June y19, 1945.

l. c.A GARDNER OPTICAL INSTRUMENT AND METHOD OF MAKING SAME Filed May 15, 1942 3 Sheets-Sheet 2 Irvine E Eprdner @M MPM @M r I I l 1 `lhune 19, 1945. l. c. GARDNER OPTICAL INSTRUMENT AND METHOD OF-MAKING SAME Filed May 13, 1942 3 Sheets-Sheet 3 gnat/wim Irvine E- E11-miner Patented June 19, 1945l :OPTICAL INSTRUMENT AND METHOD OF MAKING SAME Irvine C. Gardner, Chevy Chase, Md.

Application May 13, 1942, Serial No. '442,796

(Granted under the act of March 3, 1883,y as amended April 30, 1928; 370 O. G. 757) 7 Claims.

L The invention described herein may be manufactured and used by or for V.the Government for governmental purposes, without the payment to me of any royalty thereon.

This linvention relates to a method of pro- L'ducing optical instruments byV making the units thereof interchangeable with other similar units whereby production may be materially facilitated by obviating the necessity of the painstaking and time consuming adjustment of such units, after assembly asis required by vpresent methods.

yIt is a principal object of the invention to provide a semi-automatic method of producing optical units that will be interchangeable with vother similar units'for the purpose of assembling such units into an optical instrument.

' According topresent production methods employed inthe manufactur'erofl opticalinstruments the opticalunits or components are not interchangeablevand iinal assembly of the components into the optical instrument is an'exacting procedure requiring assembly by selection and by vthe, individual adjustment of partsthrough means of interthreaded connections, shims, etc. It is understood of course that optical tests are the `mostlexacting known and readily available to the y manufacturer with the result that it is quite pos- 'sible to make lenses or prisms which will be more nearly identical than are nominally identical mechanicaly parts. Anexample of one such test 'isthe interference test by which the curved sur- 2 facesof lenses are controlled, a test that will consistently' detect a variation of 0.000005 inch or less; however, to control all the dimensions 'of Valens with corresponding precision would unnecessarily increase the cost of the individual lenses and it is therefore customary to permit much greater departures from uniformity. The variations arising from these departures from uniformity are compensated for by present methods through selective assembly and individual adjustment as above alluded to. can be 'followed 'without any significant prejudicial effect upon the performance of the in- This procedure similar cell in an optical instrument assembled from cells similarly manufactured. As hereinbefore indicated the tolerances for the adjustvment of the optical components of an optical instrument, while small, are not zero and, for optical'instruments of the simpler type, it is possible by means of proper tooling in accordance with my method to assemble such instruments from interchangeable units by a method suggestive of the assembly line method found in automobile assembly plants.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. 1 is a longitudinal sectional viewjof a telescopic sight made in accordance with my invention and shows how the method of my invention may be applied to optical instruments in genera Fig. 2 is an exploded longitudinal vsectional view the optical units comprising the telescope of Fig. 3 is a longitudinal sectional View of a modified form of the objective shown in Fig'. 2, but is exemplary of an expedient applicable to any suitable optical unit;

Fig. 4 is a sectional view of apparatus adapted for use in my process for the purpose of cutting the optical cells or units toproper length;

Fig. 5 is aseotional View of apparatus suitable for use in centering the lens and lcell of an optical unit in accordance with the present invention; l

Fig. 6 is an elevation of the chuck shown in Fig. 5 with portions shown in section to more clearly disclose the construction;

Fig. 7 is a sectional view of apparatus adapted for use inthis invention to counterbore the objective cellof an objective unit'for the purpose 'of forming a seat for receiving and properly positioning ya reticle;

Fig. 8.is an elevational view of the structure shown in Fig. '7;

Figs. 9, l0, 1l and l2 are views showing eye` piece images as seen in the instruments used with the apparatus shown in Figs. 4 and 5, re-

spectively, for diiferent positions of adjustment of the instruments.

Referring now to the drawings there is shown in Fig. l Va telescopic instrument I0 which merely discloses by way of example how one well known type of optical instrument may be manufactured in accordance with my invention. It will be understood, however, that the method hereinafter disclosed is not limited to the manufacture of the precise instrument shown in Fig. l, but may be applied to any suitable type of optical instrument; consequently, subsequent description of the method of manufacture relative to the instrument shown is simply by way of convenience and not of limitation.

The particular telescope I shown in Fig. 1 lends itself to a comprehensive description of my manufacturing method and comprises a body tube II provided adjacent one end portion with an internal positioning seat or ilange and field diaphragm I2 and external seat 'or flange. I3 spaced a distance a toward the adjacent end of the tube therefrom. As clearly indicated in Figs. 1 and 2 the optical system of the telescope is comprised of the objective unit I4, erector units I5 and I6 and eyepiece unit I 'EL The objective and erector units are properly positioned within the body tube II in serially abutting relation to each other and to the seat I2 wherein they are so secured by the clamping ring I2 while the eyepiece unit is so arranged and dimensioned as to be properly located upon the tube Il when its forwardmost edge is disposed in abutting relation to the seat I3. f

The units I4, I5, I6 and I 'l are generally of similar construction and may be manufactured in a generally similar manner. In producing the objective unit I4 a metal cell I9 having an overall length greater than the nal length Zn shown in Fig. 2 is formed with a lens supporting flange or seat adjacent one end arranged to receive an objective lens 2| which is iirmly locked in position upon the seat by the retaining ring 22 and lock ring 23. e

The objective unit thus far formed isrnext processed to have the end 24 of its cell cut Aorf `or faced in a plane spaced from the lens equal to the distance fm-l-b` within a permissible tolerance, which in this type of instrument is usually taken to be 0.002 inch or less. The 'operation of facing the end 24 of the cell I9 may be performed in any suitable manner but is preferably done in a semi-automatic manner as by the use of apparatus as shown in Fig. 4. This apparatus comprises a hollow spindle 25- mounted for rotation in spaced bearings 26 and is adapted to be rotatably driven through any f suitable means, such as by the pulley 21 and driven belt 28. A collet chuck or similar centering means 29 preferably provided with an annular seat 39 is aflixed upon the right hand end of the spindle as viewed in Fig. 4 and a collimator 3I is mounted upon the bed of the apparatus in such manner as to direct a beam of parallel light through the hollow spindle from its end remote from the chuck in parallel axial relation, A base carriage 32 is mounted upon the bed of the apparatus for axially parallel movement of the hollow spindle and mounted upon this base carriage 32 is a second or cross feed carriage 33 arranged ior movement transversely of the base carriage movement. A suitable instrument is mounted upon the carriage 33l with its optical axis arranged in parallelism with the prolongation of the axes of collimator 3l and hollow spindle 25 whereby the instrument may have its axis arranged to coincide with the axes of the collimator and hollow spindle through movement of the carriage 33. While this instrument, which is indicated at 34,may be a. simple right angle microscope as indicated in Fig. 7 at 66, I prefer in this particular apparatus to employ a rangeinder of very short base or microscope provided with an ocular 35 that presents a divided field. With such an instrument a vertical line 36 imaged by the collimator will appear as laterally separated vertical segments as seen in Fig. 9 except when the instrument is correctly focused, at which time, the line will appear unbroken as seen ,in Fig. 10. Although the precision demanded does not require an instru- .lent of the type indicated at 34 its use will render judgment of focus less diiiicult and permit operation of the machine by operators of comparatively less experience than would normally be required. A parting or cutting off tool 3l is detachably secured to the crossI feed carriage 33 in such manner as to cut off an element retained by the chuck 29 at right angles to the axis of the spindle. For any particular optical unit being processed the tool 3l is xed in invariant longitudinally spaced relation to the instrument 34 as clearly shown in Fig. 4. By reference to Fig. 2 it will be seen that the tool 3l will be arranged to cut off the cell I9 of objective unit I4 at a distance from the objective lens 2| equal to the focal length fn -I- the distance b, the latter distance being provided for mountingreticule 38, which-is retained against its seat 39 in the focal plane of lens 2l by the retaining ring 4D and locking ring 4I.

With apparatus of the character just described the objective unit I4 will be mounted in the centering chuck 29 with its reticule end portion outermost. In this position and after the source of light for the collimator has been energized the objective lens 2| will image the collimator mark in its focal or image plane at d a distance ,fm away. The carriage 32 is next moved until the collimator mark as imaged by the objective lens is in focus in the instrument 34, which in the case of a vertical line will have the appearance of the line 36 indicated in Fig. 10. In the case of the objective unit the cutting off tool 3'I is invariantly arranged relative to the instrument 34 in such manner that when the mark imaged by the objective unit is in focus in the instrument 34 that the tool 3l will cut off and face the cell I9 at its end 24 a distance f14-I-b from lens 2| as indicated in Fig. 2. After the mark imaged by the objective lens is focused in the instrument 34 the hollow spindle 25 is rotated to rotate the objective unit I4 and the parting tool 31 is advanced by the cross feed carriage 33 to properly cut off and face the end 24 of the cell I9. It is, of course, understood that movement between the unit I4 and tool 31 need only be relative and that hence the tool may be rotated and the unit 'I4 held stationary or that the tool and unit may both be rotated at differential speeds. In Fig. 4 the chuck 29 is shown as being provided with an annular seat or stop upon which the optical unit I4 is bottomed for location in the chuck; however, this is but for convenience Asince an inaccurate setting against the stop does not introduce any error due to the fact that light incident upon lens 2| from the collimator 3l is parallel and as a result displacement of the objective unit I4 from the stop 30 will not change the fixed relative positions between the image and lens coil I9. This lack of dependence upon location of the objective unit I4 in the chuck 29 is of considerable advantage in that it increases the uniformity with which the elements may be machined. In proceeding with the processing of the objective unit in accordance with the last described process stepit will be observedl that with proper positioning'of the tool 31 upon the carriage 33 and the service of an experienced mechanic to sharpen and adjust the tool from time to time j that theapparatus may be operated by an operator relatively unskilled in the optical eld.

' .After the end 24 of the objective unit I4 has ben cut olf-and faced as above described the overall length L14 0f the cell I9 is adjusted to` proper value by cutting Aoff the end 42 thereof. The

v'flatter cutting off operation of the cell I9 may ybe ycontrolled fby any of the usual mechanical 'less' was permissible.

methods for controlling the length of a specimen.- In regard to cutting off the end 42 of cell I9`it may be noted that a tolerance of l;0.01 inch willusually 4be permissible Whereas in locating the end 24 a tolerance of only 0.002 inch or The greater tolerance in `the case of cutting the end 42 of cell I9 for controlling the overall length 114 of the cell is peryrniss'ible because the rays of light to the left of "lens 2| as viewed in Fig. 2 are parallel from an object at infinity and a variation in the spacing rbetween'thislens and the ones succeeding it has la negligible effect upon the optical performance yof the instrument; therefore, the tolerance is determined by mechanical rather than optical considerations.

The objective unit I4 after, having been thus rfarprocessed is next processed by a turning operation to ,havey the external surface' of cell .I9Y centered or provided with centered locating f surfaces arranged yconcentric tothe axis of flens 2|.\ ,For this purpose I employ apparatus -`collimator` 3| images a cross as indicated at 46 .inthese two figures. The chuck generally in- V-dlcate'd at.41 (Figs. 5 and 6) comprises a face lplate L4I!y 'bywhich it may be attached to the hollow spindle 25 through the-flange h49 on the spindle rand-bolts 50. Two slides 5| and 52 are mounted `in ways 53 and 54.for relative right 'angular movement with respect to each other. The. ways 54 which are shown disposed in a ver- 'tica'l' position in Fig.f6, are formed in or attached 'to theface plate 48 while the ways 53 are formed in the'slide block 5I. They slide block 5| is movable in the .ways 54 by a slow motion screw 55 :threadedin the face plate as shown at 56 while the jslide block 52 is movable in the Ways 53 by Jai'slow motion screw 51 threaded into the slide block 5| as indicated at 58. A slot 59 is formed lin the face plate 48 to provide for relative movement of screw 51 by reason of movement of slide blocks`5| and 52 with respect to the face plate.

y j lAn'element such 'as the objective unit I4 may be secured in the chuck by means of any suitable conventional means and it will be understood 'that vother suitable motions may be used for the vs'low'motion screws shown.

- Inthe operation of this apparatus in the stepv of'lm'aking the seating shoulders or exterior sur- 4'face of cell-I9 of the objective unit I4 concentric ,'fwith'the axis of the lens, the unit is secured in the chuck 41 and the source of light for the col- 'limator yenergized with the result that an ob- Aserverfusing the instrument 44 will see the confce'ntric lcircles 45 of the instrument and cross 46,.of the collimator imaged in superposed relafftivonin the manner indicated in Fig. 11 01 12'- If the marks image as indicated in Fig. 11 the objective unit is 'not centered and adjustment thereof will be made by means of the slow motion screws 55 and 51 until the lens 2| causes the collimator cross to stay on the circles 45 of instrument 44 in the manner indicated in Fig. 1,2 for all positions of rotation of the unit. Since the axis of the instrument 44 lies in the prolonga-I tion of the axis of the spindle 25 it will be evident that the axis of the. lens is centered with respect thereto when the condition of the marks obtains as viewed in Fig. 12 during rotation of the spindle 25 and unit I4. As soon as the unit I4 is thus centered in the apparatus it will be rotated by rotating the spindle 25, and the turning tool 60 will be advanced by the axial and cross feed carriages 32 and 33, respectively, to turn positioning .or location seats 6I on the exterior of the cell I9 concentric with the axis of lens 2|. Seats 6| may be turned on one or both ends of the cell I9 or the entire exterior surface of the cell may be turned concentric as preferred or found necessary.

The detailed explanation of the method hereinaboveset forth with respect to the objective unit is also applicable step by step with respect to the erector units I5 and I6 and eyepiece unit r I1 with slight variation.4 In the case of erector unit. I5 the end 62 thereof is cut oil and faced in thesame manner as the end 24 of unit I4; however, in this case the end 62 is cut off a distance from the lens 63' equal to its focal length fis minus the distance b vwhereby the distance between the lenses 2| and S3 in the assembled telescope will be equal to the sum of the focal lengths fir and fis, plus or minus the permissible tolerances. 'Ihe lengths Zit and lie may be controlled by the same mechanical methods employed to control length 114.

Erector unit I6 has its end 64 cut off a distance fie, equal to the focal length of lens 65, from the lens 65 and the eyepiece unit I'I has its end 65 out olf a distance from the lens G'Iequal to the focal length fn of the lens minus the distance a in order that when the eyepiece unit is secured upon the body tube II against seat I3 spaced a distance a from the focal plane of erector unit I6 that the distance between lenses 65 and 61 will be equal to the sum of their focal lengths fle land fri.

In Figs. '1 and 8 I have shown apparatus suitable for performing the final processing step on the objective unit I4, namely, the step of locating the seat 39 for the reticule 38. This apparatus is similar to the apparatus of Figs. 4 and 5, but is provided with a modiiied axial feed carriage B5 and simple right angle microscope 66 fixed thereon in' axial prolongation of the apparatus by means of the support 51. A second support 68 provided with a bore 69 is rigidly mounted on the carriage 65 in spaced relation to the support 61 with its bore in axial prolongation of the apparatus. Slidably mounted in the bore 69 of the support 58 is a hollow tool holder 10 which may be longitudinally moved to and fro in the bore 69 by means of a U-shaped stirrup 1| which is pivoted to the carriage at 12 and attached to the tool holder by pin and slot or similar connections indicated at 13. The movement of the tool holder may be limited to any value within its range of movement by a stop 14 affixed to the too! holder and a cooperating micrometer stop 15 aixed to the support l|58. A hollow counterboring tool 16 is retained in the tool holder 10 by any conventional means employed for such purpose.

In the use of this apparatus the objective unit I4 is affixed in the chuck 29 and light from the collimator 3l is caused to pass through the hollow spindle 25 and objective unit lens 2| imaging the collimator mark in the focal or proper image plane of the lens. The carriage 65 will be moved until the microscope 8B is in focus on the collimator mark image by the objective unit lens with the tool holder 'I0 and tool 'I6 in their retracted positions. The stops 14, 'I5 wil1 be adjusted to the depth of counterbore to be made,

. which in the case of objective unit I4 will be equal to the distance b shown in Fig. 2,. it being clear that the distance between the stops 14, 15 in their completely separated position and with the microscope 6G in focus on the mark imaged by the objective unit is a measure of the distance of the face of tool 'I6 from the focal plane of lens 2| of the objective unit. When the instrument 66 is in focus as described with the stops 14, 75 completely separated the unit I4 is rotated by the spindle 25 and chuck 29 and tool 16 is advanced by the stirrup 'II and tool holder 'l0 to counterbore the adjacent end of cel1 I9 to form the seat 39 against which the reticule 38 is retained by the retaining ring 40 and locking ring 4 I.

`By the method hereinabove described for forming the optical units all errors in the lenses have been compensated for by the manner in which the units have had the locating surfaces formed thereon and hence they are interchangeable in assembling which very materially facilitates production and maintenance.

The complete array of units composing the telescope are shown in Fig. 2. The body of the telescope is a straight tube II, wherein the interior positioning seat I2 also serves as a field diaphragm. The units I4, I5, and I6 are inserted in tube Il from 'its objective end in the order shown in Fig. l and crowded against each other and the seat I2 by the clamping ring or cap I8. between the two locating surfaces, the plane of the field diaphragm I2 and the shoulder or seat i3 against which the eyepiece unit I'l seats. This length can be determined by a mechanical control method and the usual tolerance permissible in this type of control will restrict the focal adjustment of the eyepiece within a range from 0 to $0.5 diopter, this being the tolerance provided for in the usual specifications for this particular type of instrument.

It may be observed that the method of assembly herein proposed also permits extremely liberal allowance of tolerances in the construction of lenses. The two optical considerations that govern limitations on tolerances in the construction of lenses are (a) aberration requirements, and (bl the focal length requirement. If the surfaces of the lens are controlled by conventional test plate methods, the index of refraction may vary as much as 0.0015 without seriously affecting the balancing of the aberrations. The usual specifications permit a variation of from l to 1.15 of the magnification. When this tolerance is distributed among all the optical components of thesystem there is still a liberal tolerance left 'for each lens, consequently my method of assembling the instrument from interchangeable units does not prohibit extremely liberal tolerances for the lenses but on the contrary makes such tolerances permissible, which is advantageous be- The dimension marked a is measured cause it permits the more effective use of available glass and favors the economic production of lenses.

Thus far in the practice of my invention I have not encountered any difliculty in permissible tolerances governing parallax; however, if the seat 39 is not accurately located it might be diflicult to eliminate this error with units constructed as in Fig. 2 so in order to make provision for an adjustment for parallax I may form the objective unit as in Fig. 3. In this form of objective unit the cell I9 is sawed to follow any suitable pattern as indicated at 68 which in effect makes the cell a stif spring which will yield when pressure is applied. The shoulder or seat 39 in this case is formed slightly to the right of the focal plane of lens 2I so that after the parts are assembled in the tube I l the cell I9 can be compressed by the clamping cap I8 to accurately position the reticule 38 in the focal plane of lens 2| and completely eliminate parallax within permissible tolerances of the instrument.

While this invention has been described in detail with respect to a specific instrument such procedure has been followed only as a matter of convenience as it will be apparent to all of those skilled in this art that a similar procedure may be followed in manufacturing various optical instruments and, therefore, I do not limit my in vention except as follows.

I claim:

1. Method for manufacturing a cell which includes a converging lens, said method comprising-introducing substantially parallel light rays into said lens in a direction substantially perpendicular to the focal plane of said lens; establishing, by operating upon the light rays which have passed through said lens, a nite point of reference from which the position of the focal plane of said lens can be reckoned; reckoning the position of a tool, for operating on said cell, from said point of reference; locating a cutting tool at said position, and relatively moving the said cutting tool and said cell to effect cutting of the latter.

2. Method for manufacturing a cell which includes a converging lens, said method comprising introducing substantially parallel light rays into said lens in a direction substantially perpendicular to the focal plane of said lens; adjustably mounting said cell for rotation about the principal axis of said lens; operating upon the light rays which pass through said lens to test the alignment of the principal axis of said lens and the axis of rotation of said cell; adjusting the position of the cell until the principal axis of said lens and the axis of rotation of the cell are in the same straight line; rotating said cell about the principal axis of said lens, and during said rotation applying a cutting tool to the said cell, whereby the resulting cut surface is concentric with the principal axis of said lens.

3. Method for manufacturing a cell containing a converging lens, the said method comprising passing parallel light rays through said converging lens, passing said rays after passage through said converging lens to a viewing instrument to be focussed by said instrument, focussing said instrument, reckoning the position of a -tool for operating on said cell from the position of said viewing instrument when in focus, locating a cutting tool at said position, and moving said cell and tool relatively to cause the said tool to operate upon the cell.

4. Apparatus `for manufacturing a cell containing a. converging lens, said apparatus comprising means for producing parallel light rays from light rays proceeding from a light source, means for mounting said cell in the path of said parallel light rays so that said light rays pass through said converging lens; optical means, utilizing the light rays passing through said converging lens, for establishing a reckoning position exterlorly of said cell from which the focal plane of said converging lens can be reckoned; a cutting tool for the material of said cell located in a position 'rreckoned 4from said established reckoning position, andv means for producing relative motion between said cell and said cutting means for operating upon the material of said cell.

5. Apparatus for manufacturing a cell con- -taining a converging lens, said apparatus cornprising means for producing parallel light rays from light rays proceeding from a light source, means for mounting said cell in the path of said parallellight rays so that said light rays pass Athrough said converging lens; optical means,

utilizing 'the light rays passing through said converging lens, for establishing a reckoning posif tion exterlorly of said cell from which the focal plane of said converging lens can be reckoned; means for rotating said cell about an axis substantially perpendicular to the focal plane of said converging lens, a lathe tool mounted for operating on said cell and located in a position reckvoned from said established reckoning position,

and means for relatively moving the said cell and said lathe tool towards and away from each other during the rotation of said cell.

6. Apparatus for manufacturing a` cell con- 1 taining a converging lens, said apparatus comprising means for producing parallel light rays from light rays proceeding from a source oi light.

means for mounting said cell in the path of said parallel light rays so that said light rays pass through said converging lens, means for rotating said cell about an axis substantially perpendicular to the focal plane of said converging lens, adjusting means for centering the principal axis of said converging lens with respect to the axis of rotation of the means for rotating said cell; optical means, utilizing the light rays passing through said converging lens, for establishing when the principal axis of said converging lens and the axis of rotation of the rotating means for the cell are concentric; a lathe tool for turn,- ing the exterior of said cell to render at least portions thereof concentric with the principal axis of said converging lens, and means for mov- `ing said tool and said cell relative to each other parallel to the principal axis of said converging lens.

7. Apparatus for manufacturing a cell containing a converging lens, said apparatus comprising means for producing parallel light rays from light rays proceeding from a source of light, means for mounting said cell in the path of said parallel light rays so that said light rays pass through said converging lens, means for rotating said cell about an axis substantially perpendicular to the focal plane of said converging lens; optical means, utilizing the light rays passing through said converging lens, for establishing a reckoning position exterlorly of said cell from which the focal plane of said converging lens can be reckoned; a boring tool located in a position lens.

IRVINE C. GARDNER. 

